Uranium (U) is an important engineering material in nuclear energy industry. Its environmental instability, however, posed challenges on its applications. Due to the active property and similar electronic configuration, Cerium (Ce) can be used as a reference metal to simulate the protection of uranium from corrosion. In order to improve the corrosion resistance of Ce, ceramic CeN, and ceramic TiN and CeN/TiN bilayer composite film were prepared by dual ion beam sputtering deposition system (DIBD). The crystal structure of films was identified by X-ray diffraction (XRD) and the chemical states of CeN film were characterized by the X-ray photoelectron spectroscopy (XPS). The Surface morphology and structure changes in atmospheric environment were examined by scanning electron microscopy (SEM) and XRD, The corrosion behavior was studied by potentiodynamic polarization and electrochemical impedance spectroscopy (EIS). The experimental results indicate the single film of CeN or TiN shows poor corrosion resistance, but the CeN/TiN bilayer composite film has better corrosion resistance. Based on the XPS, SEM and impedance analysis, we supposed that the loose of integrity and passivity breakdown on as deposited coating may be the corrosion inducement.

Corrosion resistance and mechanism of CeN, TiN and CeN/TiN bilayer composite film deposited by dual ion beam sputtering

The oxidation behavior of uranium treated by ultrasonic surface rolling process

Cleaning effectiveness to uranium surface contaminants residual using supercritical carbon dioxide(SCCO_2) fluids has been studied. Cleaning experiments mainly focusing on the general and typical machining residual contaminants such as machine oil, water and triethanolamine are carried out. By X-ray diffraction (XRD) and Auger Electron Spectrometry (AES) methods, the SCCO_2 compatibility of uranium is investigated. Results of cleaning experiments show that both machine oil and water can be dissolved by SCCO_2 and cleaned up from uranium surface easily. Triethanolamin can't be dissolved by SCCO_2. XRD study reveals that there are only U and UO_2 at cleared uranium surface. AES result indicates that during cleaning, C and O can ingress into the surface layer of uranium sample. Air corrosion test shows the uranium specimen cleaned with SCCO_2 has a better corrosion resistance than speciemen without SCCO_2 cleaning.

Study on Cleaning Technique of Uranium Specimen With Supercritical Carbon Dioxide

In this paper,the oxidation of U-2.5%Nb alloy in air at a temperature range of 60-300 ℃ was studied by measuring oxide thickness and weight gain.In addition,the morphologies were examined by using SEM.The results indicate that,under experimental condition,the oxidation of U-2.5%Nb alloy follows a parabolic law in the temperature range of 60-80 ℃,at the temperatures between 100 ℃ and 150 ℃,a para-linear law is presented,however,between 200 ℃ and 300 ℃,the oxidation obeys a linear law.At the parabolic oxidation stage,the activation energy is calculated to be 74.70 kJ/mol,and at the linear oxidation stage,which is 31.48 kJ/mol.The SEM examination reveals that,during the stage of parabolic oxidation,the "surface relief" is produced due to the difference in oxidation rate of alpha phase and gamma-two phase,but the scale is dense and compact.However,when the oxidation changes to the linear-oxidation stage,the scale becomes loose,and the vertical cracks are observed in the scale.

Oxidation of U-2.5%Nb Alloy in Air

Abstract Uranium is very important in nuclear energy industry; however, uranium and its alloys corrode seriously in various atmospheres because of their chemical reactivities. In China, continuous investigations focused on surface chemistry have been carried out for a thorough understanding of uranium in order to provide technical support for its engineering applications. Oxidation kinetics of uranium and its alloys in oxidizing atmospheres are in good agreement with those in the literature. In addition to the traditional techniques, non-traditional methods have been applied for oxidation kinetics of uranium, and it has been verified that spectroscopic ellipsometry and X-ray diffraction are effective and nondestructive tools for in situ kinetic studies. The inhibition efficiency of oxidizing gas impurities on uranium hydrogenation is found to follow the order CO2 > CO > O2, and the broadening of XPS shoulders with temperature in depth profile of hydrogenated uranium surface is discussed, which is not mentioned in the literature. Significant progress on surface chemistry of alloyed uranium (U-Nb and U-Ti) in hydrogen atmosphere is reported, and it is revealed that the hydrating nucleation and subsequent growth of alloyed uranium are closely connected with the surface states, underlying metal matrix, and it is microstructure-dependent. In this review, the recent advances in uranium surface chemistry in China, published so far mostly in Chinese language, are briefly summarized. Suggestions for further study are made.

Xinchun Lai

Papers

Recent advances in study of uranium surface chemistry in China